Pulse discrimination circuit responsive to double sets of pulses



Dec. 25, 1951 L. BESS 2,580,213

' PULSE DISCRIMINATION CIRCUIT RESPONSIVE I TO DOUBLE SETS OF PULSES Filed April 18, 1945 FIGJ INVENTOR. LEO N BES 5 A TTORNE V Patented Dec. 25, 1951 PULSE DISCRIMINATION CIRCUIT RESPON- SIVE' TO DOUBLE SETS OF PULSES Leon Bess, Boston, Mass, assignor, by'mesne as signments, to.tl1 e-,-U-nited States of America as l representedby'theSecretary'of War;

-'Application April 18, 1945, Serial No. 588,993 H a llaiipsn (Cl. 250-27)v invention 5 relates in general to control cir-:: cuits andmore. particularly to circuitsiresponsive v OIl1y tO gSet S- of control pulses 'Of predetermined characteristics. i I I Radiant energy f identification systems have been developed omprising interrogator-responsor units, containingtransmitting and receiving components, which transmit interrogating radi ant; energy pulses -to remote transponder units that also contain receiving and transmitting components and are responsive to the'interrogat;

ing radiant energy pulses. I This response is of the nature 0f identifying radiant energy signals which are transmitted backl to and received by the interrogator-responsor units to providez'the;

necessary identification. I V

Ithas been found advantageous to use trans-- ponders which are responsive only .to a predeter:

mined type of transmission so that identification.

signals will be transmitted; onlyin replylto interrogator-responsors with the proper interrogating transmission, Accordingly; it isr-one, of the ob-. jects of my invention toprovide .a circuit which canfbe in rpprated in a transponderto make it responsive only to sets of radiant energy pulses of predetermined characteristics.

It isals'oamong the objects of mylnvention to provide a control circuit which is able to discriminate betweencontrol pulsesrseparated by a predetermined timevinter val and those of difiering time separations.

.:In.general, my invention embodies a circuit which is responsive to..,a successionrof .two electriev calrpul ses spacedapart by a predetermined time interval, ,The response is of the nature of a control signal whichcan be used as a trigger or keying voltage to actuate associated. electrical apparatus.- I,

In .the application of this circuit referred to above; the receiving incomponent of the. transponder, which may be, forinstance, a super-regenerative receiver, receives, detects, and amplifiesv theradiant energy pulses transmitted by the interrogator;responsor system and supplies these pulses in video forms to the circuit herein disclosed, hereinafter referred to as aadouble pulse depoding. circuit. The double pulsedecodi'ng circuit is responsive to the video pulses, provided eri re c arat by therrq f r time n rval a'hdQgenerates a control signal which actuatesi or keys the transmitting component of the transponder so that identifying signals are transmitted to the interrogator-responsor; Such an id nt fi:

application: entitled :Electrical Apparatus?! filed AprillS, 19%5,;Seria1:No..588,994. a

My invention will best be understood jbyrefeie ence tcthe appended drawing, in which; Fig. --1 is a specific circuit diagram of adouble. pulse decoding circuit I The circuit shown in Fig. .1 includes a number of thermionic vacuum tubes; tubes 10, 20, 40,-

and 50 are triodes having anode, cathode-and control electrodes; tube 30 is a pentode having,

anode, cathode; control, screen, and V suppressor electrodes. A source of positive D.-C. plate volt age-is. provided at terminal ,I landa source-0t: D.-.C. voltage of much -less magnitude is appliedat terminal l3 to be, used'as a positivecathode;

bias voltage Terminal l 4 is: an input terminal for the application of control pu1ses.- i

QThe-plate of it b nlll is-connected through; a plateload resistor -52 to the platevoltage supply,

at -i I, andits cathode is connected to the biasing source at terminal I3, The control gridLisi coni nected through coupling capacitor IE. to the, inputterminal l4, and it is connected -to the -cathode through a grid leak resistor- I6. Connectedbef tween the-plate of ctube lfl andground is a dif ferentiating orv peakingcircuit comprising acapacitor l1, aresistor l8 and aninductancehcoil l9, which are series connected-between plate and ground in the order asirecitedr; ..This peakingcircuit operates in acconventionalgmannerto produce (sharp spikes or voltage pulses when sudden changes in applied voltage occur ras inrthe case.

of; a rectangular yoltage waveform;

QThe platefofitube 20 is-connected to the-plate l mination of: th e.line isapproximated. The oath ode of :tubelfl is connected directly to the cathode of' tube In and'thereby is provided with the-bias,- voltage from {3. fl he gridcf tube zlliisconn'ected" through resistor22 to the junction between'capacitor ll and resistor [8 in the peaking circuit.

The plateIof tube-30 is connected to the'plate oftube. 40, and its cathode is connected to ground through variable resistor 31. .The suppressor grid-ls. connected to-the cathode, the screen grid is connected to plate supply sourceatterminal ii-refine t e s. ntra e i ii.1i connecteatci mun 3 The cathode is connected to the plate of tube 20 through capacitor 23 and to the source of plate voltage ll through the series combination of resistors 32 and 33. Resistor 33 is shunted by a single pole, single throw switch 34 which is normally closed.

Tubes and 50 with their associated circuit elements comprise a multivibrator circuit. The plate of tube 40 is connected to the plate voltage source ll through resistor 4|, and the cathode is connected to ground through the series combination of resistors 42 and 43. Resistor '42 is shunted by capacitor 45 to provide a substantially constant cathode bias. connected to the junction between resistors 42 and 43 through resistor 44, and to the plate tube 50 through capacitor 54.

The plate of tube 50 is connected to the plate voltage source I I through the series combination of resistors and 52. The grid of tube 55 is connected to the source ll through resistor 53 and to the plate of tube 40 through capacitor 46. The cathode of tube 53 is connected to the cathode of tube 40. A capacitor 55 is connected from the junction of resistors 5| and 52 to the cathode of tube 50. The output is taken from terminal 51 which is connected to the junction of resistors 5| and 52 through coupling capacitor 55.

In the operation of the circuit, with switch 34 closed it is necessary to apply to terminal [4 a set of two negative control pulses which have corresponding points on their waveforms separated by a time increment equal to four times the delay time 6 which is the time that it takes a pulse to travel the length of the delay line 2|. As the first pulse is applied to the grid of tube [6, an amplified and inverted, 01' positive, pulse appears at the plate. The positive pulse is applied to the peaking or differentiating circuit comprising capacitor [1, resistor I8, and coil l9 so that by its conventional differentiating action, a sharp positive voltage spike is produced at the time that the leading edge of the pulse is applied.

Tube isnormally cut ofi by the biasing action of the positive voltage which is applied to its cathode, but when the positive voltage spike from the peaking circuit is applied to its grid, the tube conducts for the duration of the spike, and a negative pulse is initiated at its plate. This pulse travels down the delay line which has a negative reflection coefficient at the far end due to the approximate short circuit termination. The pulse is then reflected back with opposite polarity to the input terminals of the delay line. Since tube 20 is again out off after the termination of the spike on the grid, a high impedance and therefore a positive refiection coefficient is presented to the pulse as it returns after a total elapsed time of so that the pulse is again reflected but without change in polarity. The pulse again travels back to the low impedance end of the delay line, is reflected once more with a reversal of polarity, and arrives back again at the input terminals after a total elapsed time of 46 with its original polarity.

Tube is normally cut off due to the positive potential applied to its cathode by the voltage dividing action of resistors 3|, 32, and 33. This potential is adjusted by variable resistor 31 so that the magnitude of the first negative voltage pulse applied from the plate of tube 20 is not great enough to drop the cathode down to a potential permitting conduction. However, after a time 46 from the application of the first control pulse to The grid of tube 40' is.

iii

terminal I 4, the second pulse of the set is applied. This second pulse is also amplified, inverted, and peaked as was the first pulse so that when it is applied to the grid of tube 20 after the time 46, it causes a negative pulse at the plate of tube 20 that adds to the reflected first pulse, which is also present atthat time. The resultant negative pulse is of a magnitude large enough to force the cathode of tube 30 down to a potential which permits that tube to conduct for the duration of the pulse, and therefore a negative pulse appears at the plate of tube 30. The magnitude of the reflected delay line pulses is attenuated to a certain degree by the attenuating resistor 24 so that difliculty with undesired reflections after the time 45 is eliminated.

The negative pulse from tube 30 is applied to the multivibrator circuit in such a manner that tube 50, which is normally conducting, is cut off, and tube 40 starts conducting. This initiates a positive voltage wave at the cathodes of tubes 40 and 50 and at the plate'of tube 50 since the circuit elements are so chosen that tube 40 conducts more heavily than did tube 50. The duration of the positive voltage wave at the cathodes, or the relative conduction time of each tube, is determined by the associated circuit elements as in the conventional operation of triggered multivibrators well known in the art. In this particular multivibrator, because of the rising of the cathode voltagefcapacitor 55 provides a "boot strapping action by applying the positive voltage wave developed at the cathode of tube 50 to the plate of tube 50 to further increase the magnitude of the positive voltage wave developed there. Thus a large magnitude positive voltage wave is developed on tube 50, although this tube draws only a small plate current in its normal conducting condition. This positive voltage wave is applied to terminal 51 as the output control voltage which may be used as a keying voltage as suggested in the application referred to previously.

As a very brief summary of the action of this circuit, if two control pulses separated by the proper time interval are applied, a pulse is developed at the plate of tube 30 which triggers a multivibrator to produce an output control voltage.

With switch 34 closed, the circuit will not be responsive to one long pulse since no second pulse will be applied to the delay circuit from the peaker circuit after the time 45. However, with switch 34 open, tube 30 is rebiased so that a single pulse applied to the input of the circuit will develop a voltage at the plate of tube 20 large enough to cause tube 30 to conduct. Thus an output control pulse can be developed, if so desired, with a single pulse input.

It will be apparent'to those skilled in the art that changes and modifications can be made in the specific circuit herein disclosed without departing from the spirit and scope of my invention, and therefore I claim all such modifications and changes as fall fairly within the spirit and scope of the hereinafter appended claims.

What I claim is:

1 A circuit for generating a control signal upon receiving two pulses separated by a predetermined time interval comprising a differentiating network, means to impress the received pulses upon said network, a vacuum tube having at least a cathode, anode and control grid electrodes, means for impressing the output of said differentiating network on said control grid, a time delay network having a given characteristic impedance and both an input and a remote end, said input end being connected to said anode, said network being terminated at its input end by an impedance appreciably greater than said characteristic impedance and at its remote end by an impedance appreciably smaller than said characteristic impedance, said delay network having a delay interval from its input end to its remote end of one-quarter of said predetermined time interval, whereby the first of said two pulses impressed upon said difierentiating network appears as a first differentiated pulse in said anode circuit and is twice reflected back from the remote end of said time delay network to said input end, whereupon said reflected pulse will be of the same polarity as, and coincident in time with, a second differentiated pulse resulting from the application of the second of said two pulses to said differentiating network and means connected to said input end of said time delay network for deriving a control signal from said coincident reflected and second differentiated pulses.

2. A circuit for deriving a control signal from two pulse signals having a predetermined time interval therebetween comprising an electrical delay network having input terminals and terminals remote from said input terminals, a source connected to said input terminals for transmitting pulse signals to said delay network, said network being terminated at said input terminals by a substantially open circuit and at said remote terminals by a substantially short-circuit, said pulse signals being thereby reflected from both the input and remote terminals of said delay network, an electronic device, means connecting said device, to said input terminals for receiving both the reflected and unreflected transmitted pulses, means for biasing said device to a value such that it is rendered conductive only when a reflected pulse at said input terminals is of the same polarity as, and is coincident in time with, an unreflected transmitted pulse at said input terminals,

and means connected to the output of said device for deriving therefrom a control signal.

3. A circuit for deriving a control signal from two pulse signals having a predetermined time delay network, said network having an impedance mismatch at both said input and remote terminals so that said pulse signals are reflected from both said input and said remote terminals, an electronic device, means connecting said device to a given point on said network for receiving both the reflected and the impressed pulses, means for biasing said device to a value such that it is rendered conductive only when a reflected pulse at said point on said network is of the same polarity as, and is coincident in time with, an unreflected impressed pulse at said point on said network, and means for deriving a control signal from the output of said device.

LEON BESS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,061,7'34 Kell Nov. 24, 1936 2,188,970 Wilson Feb. 6, 1940 2,211,942 White Aug. 20, 1940 2,217,957 Lewis Oct. 15, 1940 2,252,599 Lewis Aug. 12, 1941 2,266,154 Blumlein Dec. 16, 1941 2,416,424 Wilson Feb. 25, 1947 FOREIGN PATENTS Number Country Date 528,192 Great Britain Oct. 24, 1940 

